502 BENNETT AND GOODYEAR 



TABLE 2 



MEAN WEIGHT (mg) FROM FIVE SAMPLE 

 POPULATIONS* OF Gambusia affinis 



*Stations PCI, PC2, and PC3 are in thermally 

 affected areas; PP and RP are in areas at natural 

 temperatures. 



Mosquitofish behavior at other stations was apparently correlated 

 with predation. Mosquitofish populations at PCS and PP were 

 confined to the shoreline by continual predation by juvenile 

 largemouth bass {Micropterus salmoides). Gambusia at Risher Pond, 

 however, were found to inhabit deeper waters, probably because of 

 relatively low predation pressure by sunfishes (Lepomis sp.). Large- 

 mouth bass are not found in Risher Pond, and sunfishes did not seem 

 to be effective predators on mosquitofish. 



The size distribution of mosquitofish collected during February, 

 June, October, and December from the various populations was 

 generally similar (Fig. 1). Populations at PP, PC2, and PCS had a 

 higher percentage of small individuals than those at RP and PCI. The 

 modal length class for each population sampled was RP, SS to 

 S8 mm; PP, PCS, and PC2, 21 to 26 mm; and PCI, 27 to 32 mm. 

 During the various collecting periods, large males were sampled from 

 populations at RP and PCS, whereas smaller average-sized males were 

 collected at PC2 and PP. Large females were collected at PCI and 

 RP, however. Although the size distributions among populations 

 were generally similar for the combined samples, larger individuals 

 were captured at different times of year (Table 2). Mean sizes of 



